A lightweight metastructure for simultaneous low-frequency broadband sound absorption and vibration isolation

We theoretically, numerically, and experimentally study a lightweight metastructure that can simultaneously reduce vibration and noise in a broad low-frequency range. We introduce spiral slits and micro-perforations in the panel and core plate of a face-centered cubic sandwich structure, respectively. A bottom-up acoustic impedance theory is developed to describe the impedance of a single unit cell. Broadband low-frequency sound absorption is achieved for a 3 × 3 supercell via reinforcement learning optimization. The resonant coupling of the upper spiral panel and the lower panel of the unit can form a wide hybridized bandgap for flexural waves, which is further validated for vibration isolation with a one-dimensional supercell. The proposed multifunctional metastructure provides a new route to design lightweight load-bearing structures with noise and vibration reduction performance for potential applications such as aerospace engineering and transportation vehicles, among others.